1. Field of the Invention
The present application relates to methods of epitaxial deposition of silicon-containing materials. More specifically, the present application relates to methods of cyclical epitaxial deposition and etch.
2. Description of the Related Art
Semiconductor processing is typically used in the fabrication of integrated circuits, which entails particularly stringent quality demands. A variety of methods are used in the semiconductor manufacturing industry to deposit material onto surfaces. One of the most widely used methods is chemical vapor deposition (“CVD”), in which atoms or molecules contained in a vapor deposit on a surface to form a film. CVD allows for the growth of films on device surface areas, including “epitaxial” films comprised of a crystalline silicon-containing material.
In some applications it may be desirable to achieve uniform or “blanket” deposition of epitaxial growth over mixed surfaces, such as insulating and semiconductor surfaces, while in other applications it is desirable to achieve “selective” deposition only over selected surfaces. Such selective deposition allows for growth in particular regions of an underlying structure by taking advantage of differential nucleation during deposition on different materials.
Selective deposition generally involves simultaneous deposition and etching of an epitaxial material. During a typical selective deposition process, a precursor of choice may be introduced that has a tendency to nucleate and grow more rapidly on one surface (e.g., a semiconductor surface) and less rapidly on another surface (e.g., an oxide surface). An etchant is added to the deposition process which has a greater effect upon the poorly nucleating film as compared to the rapidly nucleating film, therefore allowing growth on only specified surface areas. The relative selectivity of a selective deposition process is tunable by adjusting factors that affect the deposition rate (for example, precursor flow rate, temperature and pressure) and the rate of etching (for example, etchant flow rate, temperature and pressure). By precise tuning, epitaxial growth may be achieved with complete (e.g., zero growth on insulators and net growth, albeit slow, on single crystal windows) or partial (e.g., net growth on insulators and single crystal windows, with the net growth on the insulator being of lesser thickness than on the single crystal windows) selectivity on desired surfaces. However, while known processes often result in selective epitaxial growth, such growth is often of poor quality. For example, in current processes that provide selective growth in source/drain recesses, pronounced crystallographic defects may often originate in the bottom corner and sidewalls of the recess areas, resulting in undesirable, low quality epitaxial growth.
In addition to growing epitaxial material that is of high quality, it is often desirable to have epitaxial material that is strained. “Strain” may influence the electrical properties of semiconductors materials, such as silicon, carbon-doped silicon, germanium and silicon germanium alloys. Tensile strain helps to enhance electron mobility, which is particularly desirable for NMOS devices, while compressive strain helps to enhance hole mobility, which is particularly desirable for PMOS devices. Methods of providing strained material are thus of considerable interest and have potential applications in a variety of semiconductor processing applications.
It is therefore of considerable interest to provide methods of depositing epitaxial layers selectively that are of high quality and which may be strained to enhance electrical properties of semiconductor devices. It is also of considerable interest that these methods of deposition be performed efficiently to provide the added benefit of high throughput.